Method of making hydrophobic coated article, coated article including hydrophobic coatings, and/or sol compositions for use in the same

ABSTRACT

Certain example embodiments relate to a coated article including a coating formed from a sol that has hydrophobic surface properties. The sol may include a mixture of at least two alkylsiloxane chemicals, with the sol potentially being aged for a certain comparatively short amount of time before being wet-applied to a major substrate surface. The application process may also undergo a certain comparatively short curing process to help provide hydrophobic surface properties. The hydrophobic surface properties help provide anti-soiling functions that are advantageous in a variety of applications including, for example, solar mirror applications.

FIELD OF THE INVENTION

Certain example embodiments of this invention relate to methods ofproviding hydrophobic surface layers on substrate (e.g., glasssubstrates), coated articles including such hydrophobic surface layers,and sol compositions for use in the same. More particularly, certainexample embodiments of this invention relate to a method of providinghydrophobic surface coatings that provide anti-soiling, self-cleaning,and/or anti-reflection functions, coated articles including suchhydrophobic surface layers, and sol compositions for use in the same. Incertain example embodiments, a high water contact angle may be achievedusing a mixture of at least two alkylsiloxane chemicals that is aged fora short period of time, applied to a major substrate surface through asol-gel coating process, and cured for a short period of time. When suchcoatings are used in mirrors for solar applications, for example, suchhigh water contact angle coatings in certain example embodiments haveindexes of refraction compatible with the mirrors and help maintain highreflectivity by keeping the mirrors cleaner than they otherwise would bewithout such coatings.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS

Photovoltaic devices such as solar cells (and modules thereof) are knownin the art. Example solar cells are disclosed in U.S. Pat. Nos.4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, thedisclosures of which are all hereby incorporated herein by reference intheir entireties.

Substrate(s) in a solar cell/module are often made of glass. Incomingradiation passes through the incident glass substrate of the solar cellbefore reaching the active layer(s) (i.e., photoelectric transfer filmsuch as a semiconductor) of the solar cell. In particular, the poweroutput of a solar cell or photovoltaic (PV) module may be dependant uponthe amount of light, or number of photons, within a specific range ofthe solar spectrum that pass through the incident glass substrate andreach the photovoltaic semiconductor.

In order to enhance solar cell or PV absorption of light, mirrors orlenses may be applied in a solar cell system, e.g., in connection with aconcentrated solar power (CSP) system that helps to concentrate a largearea of sunlight onto a small area. Concentrated light may be convertedto heat, which may drive a heat engine (such as, for example, a steamturbine) that may be operatively connected to an electrical powergenerator to produce electrical power.

High quality mirrors are highly desirable in order to achieve moreefficiency in energy conversion. However, mirror reflections and energyconversion efficiencies are often reduced by dust and other alienparticles that adhere to the mirror surface. The particles stack on thesurface over time, and create a barrier between light and the activelayers under the surface.

It is known to address the contamination issue by using mirrors that mayexhibit hydrophobic properties. A hydrophobic mirror surface may exhibita higher resistance to the attack from dust particles by having arepelling force between mirror surface and dust particles. Hydrophobicproperties may also allow less condensation of water and fog, and reducethe likelihood of snow or other frozen material collecting on the mirrorsurface. Both functions may improve mirror reflection capabilities, andimprove power generation efficiencies.

Furthermore, hydrophobic properties of the surface may create aself-cleaning capability. The hydrophobic property may facilitate arolling action of water droplets on the surface, instead of a slidingaction. The rolling of water droplets may effectively remove the dustand unwanted particles on the surface.

Surface energy, surface roughness, and homogeneity are surfaceproperties that can be adjusted and have an impact on hydrophobicity.For example, a surface with a high degree of roughness and low surfaceenergy may show super-hydrophobicity. The highest reported contact anglefor a sessile drop of water on a smooth surface is about 120°. However,water contact angles as high as 170° has been achieved with rough andlow surface energy materials. Surface roughness produced by a fractalstructure may be a factor in the increase of contact angle for a sessiledrop of water.

Hydrophobic surfaces have been developed through numerous methods,including plasma etching, plasma deposition, laser treatment, sol-gelprocessing, anodic oxidation of aluminum, chemical etching and chemicalgrafting. Among them, the sol-gel approach demonstrates severaladvantages over other methods, such as, for example, (1) being a simplerprocess; (2) having a lower cost; (3) being more applicable to implementin a large scale production process; (4) processing at low temperature;and (5) making it easy to combine different materials.

Although hydrophobic coatings are known, further improvements are stilldesirable. For instance, it would be desirable to provide high watercontact angle coatings that have indexes of refraction compatible withthe mirrors used in solar applications (including concentrating solarpower applications) and that help maintain high reflectivity by keepingthe mirrors cleaner than they otherwise would be without such coatingsby virtue of the anti-soiling functions. In this regard, in certainexample embodiments, a method to enhance the hydrophobic properties of acoated substrate surface is provided. More particularly, the enhancementof anti-soiling and self-cleaning capabilities of surfaces becomespossible through the selection of alkylsiloxane mixtures that are agedand/or cured at different times. In addition to providing anti-soilingcapabilities, the coatings of certain example embodiments advantageouslyachieve good average total reflection and refractive index values. Inaddition, in certain example embodiments, the water contact angle ofsessile drops of water on the coated article surface corresponds to ahydrophobic coating that is in some ways comparable to surfaceproperties of a lotus leaf that allows water droplets (such as, forexample, rain drops, etc.) to roll off its surface.

One aspect of certain example embodiments relates to methods ofproviding an alkylsiloxane sol mixture and/or coating procedures thatmake a coating that exhibits hydrophobic surface properties on a majorsurface of a substrate.

Another aspect of certain example embodiments relates to a solcomposition that includes a mixture of at least two alkylsiloxanechemicals aged and cured for short periods of time, to obtain ahydrophobic property.

Certain example embodiments of this invention relate to a method ofmaking a coated article comprising a glass substrate supporting acoating. A sol is wet-applied, directly or indirectly, on a majorsurface of the substrate, the sol comprising at least first and secondalkylsiloxane chemicals, with the first and second alkylsiloxanechemicals having tetra-alkoxysiloxane and tri-alkoxysiloxane structures,respectively. The sol is dried and/or cured to form the coating. The solis aged for no more than five months prior to the wet-applying.

According to certain example embodiments, the alkylsiloxane chemicalsare provided at substantially equal weight percentages.

According to certain example embodiments, alkylsiloxane chemicals areselected from the group consisting of octyltrimethoxysiloxane (OTMOS),pentyltriethoxysiloxane (PTEOS), 3,3,3-trifluoropropyltrimethoxysiloxane (TFTMOS), tetraethyl orthosilicate (TEOS), andcombinations thereof.

Certain example embodiments of this invention relate to a method ofmaking a coated article comprising a glass substrate supporting acoating. A sol is wet-applied, directly or indirectly, on a majorsurface of the substrate, with the sol comprising TEOS and OTMOS. Thesol is dried and/or cured to form the coating. The coating has aninitial contact angle of 100-131 degrees.

Certain example embodiments of this invention relate to a method ofmaking a mirror. A thin film coating is disposed on a first majorsurface of the substrate, with the thin film coating having areflectivity of at least about 85%. A sol is wet-applied, directly orindirectly, onto the thin film coating. The sol comprises at least firstand second alkylsiloxane chemicals, with the first and secondalkylsiloxane chemicals having tetra-alkoxysiloxane andtri-alkoxysiloxane structures, respectively, and with the sol havingbeen aged for no more than three months prior to the wet-applying. Thesol is dried and/or cured to form an anti-soiling coating that at leastinitially has a contact angle of greater than 100 degrees.

According to certain example embodiments, reflection from the mirror isno more than 0.15% lower than the reflection would be if no anti-soilingcoating were present.

In certain example embodiments, a sol composition is provided. At leasttwo alkylsiloxane chemicals are provided at substantially the sameweight percents. A first alkylsiloxane chemical has atetra-alkoxysiloxane structure, and a second alkylsiloxane chemical hasa tri-alkoxysiloxane structure. The sol composition is aged less than 3months and has a cure time less than 10 minutes.

In certain example embodiments, a coated article is provided. Amulti-layer thin film coating is disposed, directly or indirectly, on afirst major surface of a substrate, with the thin film coating having areflectivity of at least about 85%. A wet-applied anti-soiling coatingis formed from a sol aged for no more than about three months prior tothe wet application and comprising tetra-alkoxysiloxane andtri-alkoxysiloxane components at least initially provided insubstantially equal weight percents. The anti-soiling coating has aninitial contact angle theta greater than 100 degrees, a refractive indexless than 1.3, a thickness of 60-100 nm, and a root mean squareroughness of 3-6.5 nm.

Certain example embodiments may relate to including a substantiallysimilar weight percentage of the alkylsiloxane chemicals in the sol. Inaddition, or in the alterative, certain example embodiments may have acuring time of preferably less than 25 minutes, more preferably lessthan 15 minutes, and still more preferably less than 10 minutes. Inaddition, or in the alternative, certain example embodiments may includean aging time of preferably no more than about five months, morepreferably no more than about 3 months, still more preferably no morethan or equal to about 1 month, prior to the wet-applying.

It will be appreciated that the example aspects, embodiments, features,etc., may be combined in any suitable combination or sub-combination toprovide yet further example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional partially schematic view illustrating alow contact angle theta of a drop on an uncoated glass substrate;

FIG. 2 is a side-cross sectional partially schematic view of the highcontact angle theta that is possible when hydrophobic coatings areprovided on a substrate;

FIG. 3 is a series of images of sessile drops of water on substratescoated with the different alkylsiloxane sols, displaying high watercontact angles;

FIG. 4A shows water droplets on a substrate coated by using a solcomprising octyltrimethoxysiloxane (OTMOS) and tetraethyl orthosilicate(TEOS) set at 80° in accordance with certain example embodiments;

FIG. 4B shows water droplets on an uncoated substrate set at 10°;

FIGS. 5A, 5B, 5C, and 5D are Scanning Electronic Microscope (SEM) imagesof an anti-soiling substrate surface in accordance with certain exampleembodiments, where FIGS. 5A-5B are partial perspective views of the toplayer at different magnifications, and where FIGS. 5C-5D arecross-sectional views at different magnifications;

FIG. 6 is a chemical reaction showing the hydrolysis of TEOS or OTMOSusing an acid catalyst in accordance with certain example embodiments;

FIG. 7 is a chemical reaction showing the condensation of hydrolyzedTEOS and OTMOS in accordance with certain example embodiments;

FIG. 8 is a chemical reaction showing the formation of cyclic siloxanethrough condensation of a tetramer in accordance with certain exampleembodiments;

FIG. 9 is a chemical reaction showing the formation of a nanoparticlewith different alkylsiloxane groups on the surface of the nanoparticlein accordance with certain example embodiments;

FIG. 10 is a schematic drawing of a hydrophobic surface of a coatedsubstrate created using an alkylsiloxane-inclusive sol;

FIG. 11 is a graph that shows the average total reflection of substratescoated with different siloxane-inclusive sol compositions;

FIG. 12 is an x-ray photoelectron spectroscopy (XPS) survey spectrum ofan anti-soiling substrate surface of sample 368-180-1;

FIG. 13 is an XPS survey spectrum of different carbon compounds insample 368-180-1;

FIG. 14 is a graph of average total reflection of substrates coated by asol and aged for one month;

FIG. 15 is a graph of average total reflection of substrates coated by asol and aged for eight months;

FIG. 16A is an atomic force microscope (AFM) image of a coating formedfrom an alkylsiloxane-inclusive sol with 50:50 wt. % of OTMOS and TEOS;

FIG. 16B is an AFM image of a coating formed from analkylsiloxane-inclusive sol with 50:50 wt. % of Pentyltriethoxysiloxane(PTEOS) and TEOS;

FIG. 16C is an AFM image of a coating formed from analkylsiloxane-inclusive sol with 50:50 wt. % of 3,3,3-Trifluoropropyltrimethoxysiloxane (TFTMOS) and TEOS;

FIG. 16D is an AFM image of a coating formed from analkylsiloxane-inclusive sol with TEOS only;

FIGS. 17A, 17B, and 17C are AFM images of anti-soiling substrate coatedwith sol and aged for one month;

FIGS. 18A, 18B, and 18C are AFM images of anti soiling substrates coatedwith sol aged and for eight months; and

FIG. 19 is a graph of average total reflection of the coated substratesin a repeatability test.

DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS

Certain example embodiments relate to a method of making an anti-soilingcoated article (such as a mirror or the like) using a sol-gel process,the sols used in such processes, and/or the coated article itself. Suchexample embodiments may be used in solar cell systems, e.g., inconnection with concentrating solar power (CSP) systems and/or the like.It will be appreciated that the term “sol-gel process” as used hereinrelates to a process where a wet formulation (referred to generally as a“sol”) having both liquid and solid characteristics is applied to theglass substrate in the form of a thin gel coating and then heated toform the final solid coating.

In certain example embodiments, sols comprising different alkylsiloxaneand silica nanoparticle inclusive sols are prepared. The sols are thenused to coat a substrate (e.g., a glass substrate supporting a Cu-basedor other mirror layer stack), e.g., to provide an enhanced anti-soilingperformance. The sols may be coated onto the substrates using anysuitable wet coating technique such as, for example, spin coating, dipcoating, roll coating, slot-die coating, meniscus coating, spraying,and/or the like.

In an exemplary embodiment, the substrate is cured in a box furnace atabout 50-400° C., more preferably 100-300° C., and sometimes about 200°C. for about 1-30 min., more preferably 3-15 minutes, and sometimesabout 5 min., to bind the alkylsiloxane and silica nanoparticles ontothe substrate surface. Without wishing to be bound by theory, it isbelieved that the covalent bond between the hydrolyzed alkylsiloxane andthe silica nanoparticles enhances the hydrophobicity of surface. Thatis, a rough surface is sought and may be generated on the surface by thesilica nanoparticles, which may improve the hydrophobicity of thesurface.

In another exemplary embodiment, the thin film coated on the surface isin the range of between about 60 nm to about 100 nm, preferably betweenabout 70 nm to about 90 nm, and most preferably between about 75 nm toabout 85 nm. The refractive index may be less than 1.5, more preferablybelow 1.3, and still more preferably below or equal to 1.23. The watercontact angle preferably is greater than 80°, more preferably greaterthan 90°, and sometimes even as high as about 130°, while average totalreflection preferably is greater than 85%, more preferably greater than90%, and sometimes about 94.20%. A durability test that involved thermalcycling and condensing humidity over 5 days showed stable optical andsurface performances. Atomic Force Microscope (AFM) images confirm thetheorized rough surfaces of the coated substrate surface. In addition,it was found that in some cases an enhanced hydrophobic substratesurface was generated by a sol with a shorter age time. By contrast, asol with a longer age time may reduce the amount of alkylsiloxane groupson coated surface by hydrolysis and condensation process of siloxane,thereby reducing the hydrophobicity of the substrate's surface.

Example techniques for creating sols in accordance with certain exampleembodiments, and methods for evaluating coated articles produced usingsuch sols (e.g., in connection with providing an improved hydrophobicsurface layer), are discussed below.

Example Sol Compositions

The sol-gel mixtures used in the examples set forth below includedoctyltrimethoxysiloxane (OTMOS), pentyltriethoxysiloxane (PTEOS), and/or3,3,3-trifluoropropyl trimethoxysiloxane (TFTMOS). Tetraethylorthosilicate (TEOS, Aldrich), N-propyl alcohol (NPA, Aldrich), aceticacid (AcOH, Fischer), and nano silica particles (IPA-ST-UP, 15% in IPA,Nissan Chem.) were used in the process without purification. Deionizedwater with a conductivity of about 18 Ω/cm, and nitrogen gas, also wereused in the process. The sols were coated onto substrates supportingCu-based mirror coatings, and the substrates were 4 mm thick glasssubstrates. Three paints were provided to the back surface, asmanufactured by Guardian. It will be appreciated that other substrates(e.g., different substrate types, different thicknesses, etc.) and/ormirror coatings may be used in connection with different exampleembodiments.

Sols were prepared with different alkylsiloxane materials in themixture. In certain example embodiments, the adhesive strength of silicananoparticles on a substrate surface can be improved when a 50 wt. %TEOS material is used with a tetra-alkoxysiloxane structure mixed with atri-alkoxysiloxane structure. Exemplary compositions of sols, with TEOSas a basic binder, are compared in Tables 1 to 4.

TABLE 1 Formulation of sol with octyltrimethoxysiloxane (OTMOS) andtetraethyl orthosilicate (TEOS) as binders M.W. Chem. (g/mol) Wt, g Wt.% NPA 60.1 34.852 69.809 Deionized water 18 0.904 1.811 Acetic acid(AcOH) 60.05 2.444 4.896 Octyltrimethoxysiloxane 234.41 0.909 1.821(OTMOS), 50 wt. % Tetraethyl orthosilicate 208.33 0.909 1.821 (TEOS), 50wt. % Nano silica particle — 9.974 19.978 (IPA-ST-UP) Total — 50 100

TABLE 2 Formulation of sol with pentyltriethoxysiloxane (PTEOS) andtetraethyl orthosilicate (TEOS) as binders M.W. Chem. (g/mol) Wt, g Wt.% NPA 60.1 34.852 69.809 Deionized water 18 0.904 1.811 Acetic acid(AcOH) 60.05 2.444 4.896 Pentyltriethoxysiloxane 234.41 0.909 1.821(PTEOS), 50 wt. % Tetraethyl orthosilicate 208.33 0.909 1.821 (TEOS), 50wt. % Nano silica particle — 9.974 19.978 (IPA-ST-UP) Total — 50 100

TABLE 3 Formulation of sol with 3,3,3-trifluoropropyl trimethoxysiloxane(TFTMOS) and tetraethyl orthosilicate (TEOS) as binders M.W. Chem.(g/mol) Wt, g Wt. % NPA 60.1 34.852 69.809 Deionized water 18 0.9041.811 Acetic acid (AcOH) 60.05 2.444 4.896 3,3,3-Trifluoropropyl 234.410.909 1.821 trimethoxysiloxane (TFTMOS), 50 wt. % Tetraethylorthosilicate 208.33 0.909 1.821 (TEOS), 50 wt. % Nano silica particle —9.974 19.978 (IPA-ST-UP) Total — 50 100

TABLE 4 Formulation of sol with tetraethyl orthosilicate (TEOS) asbinders M.W. Chem. (g/mol) Wt, g Wt. % NPA 60.1 34.852 69.809 Deionizedwater 18 0.904 1.811 Acetic acid (AcOH) 60.05 2.444 4.896 Tetraethylorthosilicate (TEOS) 208.33 0.909 3.764 Nano silica particle (IPA-ST-UP)— 9.974 19.978 Total — 50 100

An exemplary procedure to prepare the sols listed in Tables 1 and 4 isas follows: 1) 34.852 g of NPA is added into a 200 ml glass bottle witha magnetic bar; 2) 0.904 g of deionized water, 0.909 g of OTMOS, 0.909 gof TEOS and 9.974 g of IPA-ST-UP is added to the NPA to form a mixture;3) 2.444 g of acetic acid is added to the mixture to create a solution;and 4) the solution is stirred immediately at room temperature for about24 hours before using. The example sols listed in Tables 1, 2 and 3 wereaged 24 hours before usage. The example sol composition listed in Table4 was aged at room temperature for two separate aging times: one monthand eight months. There was no precipitation in any of the example solsduring the preparation and storage periods.

The sols used to coat the substrates were colloidal solutions thatincluded elongated SiO₂ nanoparticles and tetraethyl orthosilicate(TEOS) as a binder. One specific type of sol used in this disclosure asthe comparable baseline is the TEOS-only sol composition listed in Table4. The solid weight percent of sol are noted herein. However, thepercentages may vary under desired conditions and parameters, and arenot limited to the values presented in this disclosure.

Example Substrate Preparation and Coating Procedures

Conventional pre-cleaning and/or washing steps may be used to prepare asubstrate for coating using relatively weak acid and base solutions. Anexample procedure may include the following steps: 1) dipping asubstrate into a mixture of an HCl solution of about 2% concentrationand an HNO₃ solution of about 2% concentration for about 10 minutes; and2) washing the dipped substrate with a soap solution and deionizedwater; and 3) drying the washed substrate using N₂ gas. The cleaningprocess could be also implemented by plasmas, electron beam, ultrasonic,and/or glow discharge related techniques. However, it will beappreciated that other pre-cleaning and/or washing procedures includingthe use of other concentrations and/or types of cleaning solutions maybe possible in different implementations.

An exemplary procedure to coat a substrate using the siloxane-inclusivesol mixtures disclosed herein, including the example sol mixturesdisclosed in Tables 1 to 4 above, for example, may include spin coating,dip coating, roll coating, slot-die coating, meniscus coating, and/orthe like. When a spin-coater is used, the following conditions may beimplemented to create a suitable coating: 1) mounting a substrate on asample stage of a spin coater; 2) placing a specific amount of sol(e.g., about 0.5 mL) onto a top surface of the substrate; 3) spinningthe substrate at a suitable speed with an optional suitable ramp andsuitable spin time (e.g., about 3000 rpm with a ramp speed of about 255rpm, and a spin time of about 30 sec); and 4) setting the coatedsubstrate in a furnace (e.g., at about 200° C. for about 5 min.) inorder to cure the sol on the substrate surface. The curing of thin filmcould be also processed by IR, UV, and/or microwave related techniques,which may in some instances provide more controllable features. It willbe appreciated that other suitable procedures and/or process conditionsmay be used to create a similar thin-film coating. For instance, theexample cure temperatures and/or times identified above may be used incertain example embodiments.

Example Evaluation Procedures

Samples generally may be evaluated using conventional methods applicableto the particular sample produced and other conditions and limitationsto be imposed onto the sample. Example measurement techniques anddevices including those used herein are set forth below. However, itwill be appreciated that other evaluation procedures, equipment, etc.,may be used in different cases.

Broadband reflection of coated substrates may be measured using a UV-Visspectrophotometer such as, for example, the PerkinElmer LAMBDA 1050UV/Vis/NIR Spectrophotometer. The broadband spectrum of between 300 nmand 2500 nm is used herein, although other spectra may be used indifferent caes. The average total reflection, R %, may be calculatedusing Eq. (1):

$\begin{matrix}{{R\mspace{14mu} \%} = \frac{\sum\limits_{i = 300}^{2500}\; {{\rho_{h}( {\lambda_{i},\theta,h} )}{E_{\lambda}( \lambda_{i} )}{\Delta\lambda}_{i}}}{\sum\limits_{i = 300}^{2500}\; {{E_{\lambda}( \lambda_{i} )}{\Delta\lambda}_{i}}}} & (1)\end{matrix}$

where ρ_(h) (λ, θ, h) is hemispherical reflection spectrum; F_(λ)(λ_(i)) is direct solar irradiance spectrum, and Δλ is wavelengthinterval. The wavelength interval is 5 nm. It will be appreciated thatother formula may be used, e.g., where different spectra are involved.

The reflection gain of the sol coated substrates, ΔR %, may becalculated by: 1) subtracting R % of raw mirror glass from R % of coatedmirror glass in the case of developed mirror glass as shown in Eq. (2);and 2) subtracting from pre R % of coated mirror glass from post R % ofcoated mirror glass in the case of durability test as shown in Eq. (3).

ΔR %_(|Optical)=(R %)_(coated)−(R %)_(raw)   (2)

ΔR %_(|Durability)=(R %)_(postcoated)−(R %)_(precoated)   (3)

Measurement of water contact angle of a drop (e.g., a sessile drop) onthe substrate may be conducted using a contact angle instrument such as,for example, a First Ten Angstroms device 136 for the measurement ofcontact angles of a sessile drop (FTA 136). A sessile drop of de-ionizedwater, e.g., about 6 μl, may be wetted on the substrate surface, and thecontact angle of the drop may be measured immediately thereafter. Thedata reported below corresponds to the average values measured fromthree points on a substrate surface. Calculations of the contact angleswere performed using the First Ten Angstroms measurement software,version 1.966.

Optical thickness and refractive index of the coated substrate may bemeasured using an Ellipsometer (such as the J. A. Woollam Co., HS-190device). The mirror sample may be scanned with multiple angles in orderto measure the complex reflectance ratio, ρ which is parameterized by Ψand Δ. The refractive index of coated substrate may be reported at thewavelength of 550 nm, although different wavelengths are of coursepossible.

The topography of the surface of the coated substrates may beinvestigated qualitatively using an atomic force microscope (AFM, e.g.,the AP-0100, Parker Sci. Instrument). The non-contact method, preferredfor soft surfaces in general, may be used in some cases. The size ofmirror sample may be about 1 cm×1 cm and the scanning area may be about5 μm×5 μm. The scanning rate used herein is 0.5. The sample roughnessmay be characterized quantitatively by measuring the arithmetic averageroughness, R_(a), and root mean square roughness, R_(m), R_(a) and R_(m)are described in Equations (4) and (5), below.

$\begin{matrix}{R_{a} = {\frac{1}{n}{\sum\limits_{i = 1}^{n}\; {y_{i}}}}} & (4) \\{R_{m} = \sqrt{\frac{1}{n}{\sum\limits_{i = 1}^{n}\; y_{i}^{2}}}} & (5)\end{matrix}$

where y_(i) is the height of peak in AFM image.

The morphologies of the anti-soiling glass may be observed by using ascanning electronic microscope such as, for example, a Hitachi S4800field emission SEM. The working distance used was 4.0 mm and 6.7 mm forimages with top surface, with a rotated position of 45 degrees. Themeasurements were taken using a tungsten coated layer with a thicknessof between 5 nm and 10 nm on the surface of the present samples. Theaccelerating voltage for the measurements was 30 kV.

An x-ray photoelectron spectroscopy (XPS) spectrum of anti-soilingmirror may be analyzed using an X-ray photoelectron spectroscope such asthe PHI Quantera XPS, with a monochromated Alk_(α) as x-ray source, anda voltage of 1486.6 eV. An analyzed area of each of the examplesubstrates was about 1.5 mm×1.5 mm, using a charge correction in C1s(C—C/C—H) of 284.8 eV.

A variety of durability tests also may be performed. For instance,durability may be measured using a high-temperature/high-humidity(HT-HH) or condensing humidity test, a thermal cycling test, and/or thelike. During the condensing humidity test, coated substrates having asize of 2″×2″ are placed vertically onto a plastic sample holder. Thesample holder is subjected to 85° C. temperatures at 85% relativehumidity (although higher or lower temperatures and/or relative humidityvalues may be used in different test scenarios). The substrates are thenremoved from the chamber, washed with deionized water, and tested withan UV-vis spectrophotometer for reflection capabilities. A surfaceperformance test measurement of water contact angles also may beperformed (e.g., using the FTA 136 as noted above). In general, a samplemay pass the condensing humidity test if the calculated AR% is less thanor equal to 1%, and has no visual damage in the surface coating.

Thermal cycling tests also may be performed, e.g., in connection with2″×2″ coated substrates that are placed vertically onto a plastic sampleholder. The sample holder is subjected to a variation of humidity andtemperature ranges. The temperature is first raised from about 25° C. toabout 85° C. within about 1 hour, with a humility range of about 50% toabout 85%. The temperature is held at about 85° C. for about 20 hoursbefore it is decreased to about −40° C. for about 1 hour. Thetemperature is then raised from −40° C. to 25° C. within about 0.5hours, and then raised from 25° C. to 85° C. to complete one thermalcycle. It will be appreciated that other temperature values and/or rampsmay be used in different test scenarios. In general, a sample may passthe thermal cycling test if the calculated ΔR % is less than or equal to1%, and has no visual damage in the surface coating.

As indicated above, the measuring techniques and apparatuses describedabove are examples that could be used to measure example embodiments. Itwill be appreciated that other suitable measuring techniques,procedures, and/or apparatuses may be used in connection with otherapplicable conditions and parameters to assess example embodimentsproduced in accordance with the techniques disclosed herein. Exemplaryresults of the disclosed examples using the parameters described aboveare presented in the following tables and figures.

Example Sample Evaluation Results I. Water Sessile Drop Contact Anglesand Mobility

In FIGS. 1 and 2, water contact angles are depicted for a sessile dropof water 101 on a surface 102. The water contact angle is measured as θ.FIG. 1 is a side cross-sectional partially schematic view illustrating alow contact angle theta of a drop on an uncoated glass substrate, andFIG. 2 is a side-cross sectional partially schematic view of the highcontact angle theta that is possible when hydrophobic coatings areprovided on a substrate.

Table 5 lists the water contact angle of substrates coated by sols withdifferent siloxane mixtures in the present example, the composition ofwhich is shown above in Tables 1 to 4. Measured water contact angles ofthe coated substrates are in the range of about 108° to about 131°,depending on the sol composition. Water contact angles are measuredusing a sessile drop of water and equipment such as the FTA 136.Compared to the water contact angle of an uncoated substrate, whichtypically is about 20°, the increase in the water contact angle ofcoated substrates may be attributed to the alkylsiloxane groupcovalently attached onto the substrate surface. The order of the watercontact angles in the present example is: OTMOS (131°)>PTEOS(120°)>TFTMOS (113°)˜TEOS (108°). This shows that an increase on thecarbon number of alkylsiloxane compound, which corresponds to anincrease of hydrophobicity of the siloxane mixture, enhances thehydrophobicity of the substrate surface.

TABLE 5 Water contact angle of substrates coated using sols withdifferent alkylsiloxanes wt. % R % R % ID Siloxane in sol of sol Contactangle avg. STD 368-180-1 Octyltrimethoxysiloxane 2 117.51 146.92 128.96131.13 14.82 (OTMOS)/TEOS (50:50 wt. ratio) 368-180-2Pentyltriethoxysiloxane 2 123.64 118.17 120.23 120.68 2.76 (PTEOS)/TEOS(50:50 wt. ratio) 368-180-3 3,3,3-Trifluoropropyl 2 119.48 109.81 110.39113.23 5.42 trimethoxysiloxane (TFTMOS)/TEOS (50:50 wt. ratio) 368-180-4Tetraethyl orthosilicate 2 103.95 119.1 103.67 108.91 8.83 (TEOS) Agedtime of sol < 1 month Spin coating: 3000 rpm; 255 ramp; 30 sec; 0.5 mlof sol Curing at 200° C. for 5 min

FIG. 3 is a series of images of sessile drops of water on substratescoated with the different alkylsiloxane sols, displaying high watercontact angles.

The hydrophobicity of the substrate surface is further confirmed by themobility of water droplets compared between a coated substrate surfaceand an uncoated substrate surface. Mobility tests were conducted wherewater droplets were placed on a coated substrate surface and an uncoatedmirror. Both substrates were set on a table at different level angles.FIGS. 4A and B are schematic drawings of the movement of the waterdroplets on the two types of surfaces. In FIG. 4A, water droplets 401are seen to adhere to a coated surface 403 set at an 80° angle withrespect to the horizon and stay in a droplet shape. Characteristics ofwater droplets 401 with a near-spherical form on a hydrophobic surface403 may allow water droplets 401 to roll across the surface 403, andpick up the alien particles 402.

In comparison, in FIG. 4B, water droplets 401 are not able to adhere toan uncoated surface 404 set at a 10° angle with respect to the horizon.Instead, the water droplets 401 on the uncoated surface 404 slid quicklyto the bottom of the surface 404, and then accumulated at the bottom. Itis believed that the adherence property is due to the hydrophobicity ofa coated surface. It is also believed that the rough and nano-scale “dotstructure” on the coated surface may also act to trap air underneath thewater droplets, which may enhance the rolling motion.

II. Morphology

Results of an SEM morphology investigation of the coated substrates areshown in FIGS. 5A, 5B, 5C, and 5D. The hydrophobic characteristicsdisplayed by water droplets on a coated surface can be explained using amorphology of the coated surface. FIGS. 5A, 5B, 5C, and 5D are SEMimages of a substrate surface coated by the sol mixture listed in Table4. FIG. 5A shows the morphology of a top layer of the surface in a 25Kmagnification, and FIG. 5B shows the morphology of the same top layer ofthe surface in a 100K magnification. FIG. 5C shows a cross-sectionalview of the top layer at a 100K magnification, and FIG. 5D shows across-sectional view of the top layer at a 200K magnification.Substantially uniform nano-dots with a diameter of around 20 nm isclearly observable on the substrate surface. Morphology of thenanoparticle coated substrate is found to be similar to a morphology ofa lotus leaf. Because of the similarity in morphology observed, it isbelieved that the nanoparticle coated substrate surfaces may exhibitsimilar hydrophobicity characteristics as the lotus leaf in allowingwater droplets to roll off the contact surface.

Formation of an anti-soiling coating layer on the surface of a substratein the present example can be described using chemical reactions thatoccur during a sol-gel coating process. TEOS and/or other siloxanes(e.g. OTMOS) can be hydrolyzed by SN₂ mechanisms in the presence of anacetic acid. FIG. 6 shows the expected hydrolysis process of siloxanes,i.e. TEOS and OTMOS, with acetic acid as a catalyst. First, theelectrophilicity of the Si atom is enhanced by the attack of a proton,H⁺, which is released from the acetic acid to the OR group of thealkylsiloxane. The intermediate as shown in FIG. 6 is generated by thereaction of water with a Si atom. The reaction intermediate produces thehydrolyzed siloxane and releases one alcohol molecule and one proton,H⁺, which can be recycled as a catalyst again. This process may berepeated to generate various fully hydrolyzed siloxane, i.e. silicicacid Si(OH)₄. In addition, the esterification might be one reversiblereaction existing in the hydrolysis.

It is further believed that the condensation of hydrolyzed TEOS or OTMOScan be condensed by water and alcohol condensation, e.g., as shown inFIG. 7. During the condensation process, cyclic siloxane with differentcyclic numbers may be formed by partially condensed TEOS and OTMOS, suchas, for example, the tetra-cyclic siloxane shown in FIG. 8. It isbelieved that a primary cyclic siloxane is generated from the tetramerbecause of a lesser strain on the cyclic compound.

Then, as shown in FIG. 9, amorphous SiO₂ particles with a continuousrandom network structure and alkylsiloxane groups on the surface ofnanoparticles can be generated by a reaction between a cyclic siloxaneand a hydrolyzed siloxane. The three-dimensional particles may serve asnucleation sites and further growth may occur by an Ostwald ripeningmechanism, whereby the particles grow in size and decrease in number ashighly soluble small particles dissolve and re-precipitate on larger andless soluble nuclei. Growth may stop when the difference in solubilitybetween the smallest and largest particle becomes only a few ppm. Moregenerally, the particle may grow to the size of at least about 1 nm,preferably between about 1 nm to about 5 nm, more preferably betweenabout 2 to about 4 nm, and with precursor solution of pH between about 1to 8, preferably about 2 to about 7, and more preferably about 3 to 5.Specifically, the particle may stop the growth when it reaches the sizeabout 2 to about 4 nm with precursor solution of pH about 2 to about 7.As a result, a substrate surface coated by the sol mixtures, e.g., thesol compositions listed in Table 1 to 4, may exhibit variousalkylsiloxane groups and chains attached onto the surface of a substrateas shown in FIG. 10. The nano dots 1001 from the nano-particles in thesol coats the substrate glass, while the alkylsiloane chain groups 1002extend from the substrate surface to create a rough surface.

III. Reflection

FIG. 11 is a graph that shows the average total reflection of substratescoated with the siloxane-inclusive sol compositions of Tables 1 to 4above. It will be appreciated that the reflection curves display almostthe same pattern for each of the alkylsiloxane sols.

IV. X-Ray Photoelectronic Spectrum

XPS spectrum measurements of the coated substrates in the presentexample are presented in FIG. 12. Other than the elements oxygen (O 1sand O 2s) and silicon (Si 2s and Si 2p), carbon (C 1s) is detected,providing a binding energy of about 284.8 eV. A more detailed XPSspectrum shown in FIG. 13 displays the different carbon compounds thatare present. In order to compensate for surface charge effects, bondingenergies are calibrated using the C 1 s hydrocarbon peak at 284.8 eV.The binding energy shown from 286.3 eV to 286.5 eV is from a C—O group,and the range shown from 287.8 eV to 288.0 eV can be attributed to a C═Oor O—C—O group. Finally, the binding energy of O═C—O group is in therange between 288.9 eV to 289.1 eV. The binding energy of Si—O in theSiO2 compound, and/or O in an organic group, is located in the rangebetween 532 eV to 533 eV.

Table 6 lists the composition of the different elements analyzed by theXPS. It will be appreciated that apart from oxygen and silicon elements,many carbon species are found on the coated surface. The high-resolutionSi 2p spectrum shows that the Si present is from silica (SiO₂), asexpected. The C1s spectrum shows that there is a main hydrocarbon(C—C/C—H) component, which is a contribution from the oxidizedfunctional groups (C—O, C═O/O—C—O and O═C—O). The contributions ofvarious carbon bonds to C 1s, derived from the C 1s curve-fitting, aresummarized in Table 7.

TABLE 6 Atomic concentrations Atomic. % ID C O Si 386-180-1 21.1 55.423.5

TABLE 7 Composition of carbon compound Chem. species C—C/C—H C—OC═O/O—C—O O═C—O % 84 14 1 1

V. Thickness and Refractive Index

The thickness and refractive index of the coated substrate surfaces aremeasured and summarized in Table 8. That is, table 8 lists the thicknessand refractive index of the substrate surface coated by sols composed ofdifferent alkylsiloxane. The coating layer is a typical thin film withanti-reflection characteristics. In certain example embodiments, thecoating will have a thickness of preferably about 60 nm to about 100 nm,more preferably about 70 nm to about 90 nm, and most preferably about 75nm to about 85 nm. However, in other example embodiments, the thicknessmay be higher or lower. The coating may have a refractive indexpreferably of less than 1.5, more preferably below 1.3, and morepreferably below or equal to about 1.23. Specifically, the presentexample involves a coating with a thickness of about 80 nm, and arefractive index in the range between about 1.201 to about 1.238.

TABLE 8 Thickness and refractive index of substrate surface coated usingsols with different alkylsiloxanes Thickness Refractive ID Siloxane insol (nm) index (550 nm) 368-180-1 Octyltrimethoxysilane 86.39 1.223(OTMOS)/TEOS 50:50 wt. ratio 368-180-2 Pentyltriethoxysilane 78.6181.201 (PTEOS)/TEOS; 50:50 wt. ratio 368-180-3 3,3,3-trifluoropropyl80.47 1.233 trimethoxysilane (TFTMOS)/TEOS; 50:50 wt. ratio 368-180-4Tetraethyl orthosilicate 87.08 1.238 (TEOS) Solid wt. % = 2 wt. % Agedtime of sol < 1 month Spin coating: 3000 rpm; 255 ramp; 30 sec; 0.5 mlof sol Curing at 200° C. for 5 min

Effects of Sol Aging Time and Curing Time

Effects of sol aging time is evaluated in the present example throughthe assessments of the water contact angles of sessile drops of water,and the broadband reflection of the coated substrate surfaces ofdifferent sol compositions.

The TEOS-only sol in Table 4 was split into two batches, and separatelyaged for one month and eight months at room temperature before beingcoated onto a substrate. Table 9 summarizes the water contact anglemeasurements of coated substrate surfaces with different solcompositions with the different aging times. The results show that ahydrophobic surface may be achieved with a short aging time because alower water contact angle of substrate coated by sol aged for eightmonth is observed. It is believed that a sol with a longer aging timemay contain a lower amount of TEOS that is only partially hydrolyzed,which can result in a surface with a lower amount of alkylsiloxane groupchains. In that case, a hydrophilic surface may be observed.

TABLE 9 Water contact angle of substrate coated using sols withdifferent age times Aged wt. % time ID of sol (Month) Contact angle Avg.STD 368-172-1 1 1 117.81 112.60 134.12 121.51 11.23 368-172-2 2 1 113.07108.35 112.07 111.16 2.49 368-172-3 3 1 119.80 107.19 99.65 108.88 10.18368-174-1 1 8 10.74 9.31 10.23 10.09 0.72 368-174-2 2 8 16.52 20.1124.19 20.27 3.84 368-174-3 3 8 12.90 6.95 10.47 10.11 2.99 Spin coating:3000 rpm; 255 ramp; 30 sec; 0.5 ml of sol Curing at 200° C. for 5 min

Broadband reflections of coated substrates with the TEOS-only sols ofdifferent aging times are summarized in Table 10 as the calculatedaverage total reflections. The calculated values are also presented inFIGS. 14 and 15. The results show that there is no substantial changebetween reflections of substrate surfaces coated by sols with differentaging time. The hydrophobic or hydrophilic properties observed on thesurface do not seem to alter the reflection on the substrate. Generally,R % of the uncoated mirror is about 94.24%; coated substrates as alsosubstantially the same as the uncoated mirror. The R % gain preferablyis no less than about 0.15% lower than the uncoated mirror for the agingtime of eight months, and more preferably no less than 0.11% lower thanthe uncoated mirror for the aging time of one month.

TABLE 10 Reflection of substrates coated with sols with different agetimes Sol Aged time, R R ID wt. % (Month) % % gain uncoated 0 94.24 —mirror 368-172-1 1 1 94.24 0 368-172-2 2 1 94.25 0.01 368-172-3 3 194.13 −0.11 368-174-1 1 8 94.1 −0.14 368-174-2 2 8 94.18 −0.06 368-174-33 8 94.19 −0.05 Spin coating: 3000 rpm; 255 ramp; 30 sec; 0.5 ml of solCuring at 200° C. for 5 min

In addition, the effect of curing time on a substrate surface ismeasured against the optical performance of the substrate surface. Thepresent example investigates coated substrates made at different curingtimes at about 200° C. Table 11 summarizes the water contact angle ofsubstrates cured at 200° C. with curing time at about 5 minutes andabout 30 minutes. The results show that generally, the water contactangle decreases with an increase in curing time, except for substratescoated by sol with only TEOS. Results show that thermal degradation ofalkylsiloxane may occur at a high temperature and a long curing period.It is believed that the decomposition probability of alkylsiloxanegroups may depend upon the length of the alkylsiloxane chain, whichindicates that longer alkylsiloxane chains may be more likely todecompose. This may explain results in a decrease of water contact anglefound on the substrate surfaces coated by sols with longer alkylsiloxanechain groups after a long curing time.

In certain example embodiments, the coated substrates may be cured at atemperature range of about 150° C. to about 250° C., preferably for lessthan 25 minutes, more preferably less than 15 minutes, still morepreferably less than 10 minutes

TABLE 11 Effect of curing time on water contact angle of substratescoated using sol with alkylsiloxanes Contact angle, θ 200° C., 200° C.,ID Siloxane in sol 5 min 30 min Change 368-180-1/5Octyltrimethoxysiloxane 131.13 103.68 −27.45 (OTMOS)/TEOS 50:50; wt.ratio 368-180-2/6 Pentyltriethoxysiloxane 120.68 85.08 −35.60(PTEOS)/TEOS; 50:50; wt. ratio 368-180-3/7 3,3,3-Trifluoropropyl 113.2373.19 −40.03 trimethoxysiloxane (TFTMOS)/TEOS; 50:50; wt. ratio368-180-4/8 Tetraethyl orthosilicate 108.91 106.75 −2.15 (TEOS)

Calculations of the average total reflection of coated substratesurfaces are summarized in Table 12, and are observed to be independentof curing times. Table 12 shows that there are no significant changesbetween the two sets of samples with different curing times for thesesamples.

TABLE 12 Effect of curing time on reflection of substrates coated usingsol with different alkylsiloxanes R % 200° C., 200° C., ID Siloxane insol 5 min 30 min Change 368-180-1/5 Octyltrimethoxysiloxane 93.25 92.77−0.48 (OTMOS)/TEOS 50:50; wt. ratio 368-180-2/6 Pentyltriethoxysiloxane93.42 93.48 0.06 (PTEOS)/TEOS; 50:50; wt. ratio 368-180-3/73,3,3-trifluoropropyl 94.24 94.17 −0.06 trimethoxysiloxane(TFTMOS)/TEOS; 50:50; wt. ratio 368-180-4/8 Tetraethyl orthosilicate93.36 93.27 −0.09 (TEOS)

AFM images of the different coated substrates are also compared byassessing the effects of the different alkylsiloxane on the morphologyof coated substrates surfaces, and the effects of different aging timesof sols on the morphology of substrate surfaces.

Furthermore, the effect of alkylsiloxane on morphology of coatedsubstrates in the present example are presented accordingly in FIGS.16A, 16B, 16C, and 16D, using AFM images of the coated substratesurfaces. The root mean square (RMS) roughness of certain exampleembodiments may be about 3 nm to about 6.5 nm, preferably between about4 nm to about 5 nm, and more preferably between about 4.5 nm to about4.2 nm. Roughness of the coated surfaces of certain samples wereestimated using R_(a) and R_(m), and the results are summarized in Table13, labeled accordingly. The results show that there is no significantdifference on surface roughness on coated substrate surfaces by solswith different alkylsiloxane mixtures. However, similar roughness ofcoated substrate surfaces may be attributed to the fact that the carbonnumbers of alkylsiloxane compounds used in this study are similar toeach other, which may cause the result of the similar morphology of thesurfaces shown in FIGS. 16A, 16B, 16C, and 16D. The morphology of coatedsubstrate surface by the sol is believed to be dominated by thestructure and form of the silica nanoparticles coated onto the substratesurfaces. This is believed based on the observation of the measured bondlength of C—C of only 0.154 nm, in comparison to the thickness of thesilica nanoparticle of about 80 nm shown in Table 6 above.

TABLE 13 Ra and Rm roughness of anti-soiling substrates made usingdifferent alkylsiloxanes Ra Rm ID Siloxane in sol wt. % (nm) (nm) 368-Octyltrimethoxysiloxane 2 3.251 4.231 180-1 (OTMOS)/TEOS; 50:50; wt.ratio 368- Pentyltriethoxysiloxane 2 3.270 4.169 180-2 (PTEOS)/TEOS;50:50; wt. ratio 368- 3,3,3-trifluoropropyl 2 3.272 4.121 180-3trimethoxysiloxane (TFTMOS)/TEOS; 50:50; wt. ratio 368- Tetraethylorthosilicate 2 4.448 5.894 180-4 (TEOS) Spin coating: 3000 rpm; 255ramp; 30 sec; 0.5 ml of sol Curing at 200° C. for 5 min

An assessment of the effect of aging time of sols in the presentexample, one month and eight months, is performed through a measurementof the AFM morphology of the substrate surfaces, and the results aresummarized in Table 14. FIGS. 17A, 17B, and 17C are AFM images ofanti-soiling substrate coated with sol and aged for one month, and FIGS.18A, 18B, and 18C are AFM images of anti soiling substrates coated withsol aged and for eight months. The increase of roughness is observedwith the surface of substrates coated by sol with longer aged time. Thevalue of R_(m) for substrates coated by sol aged for eight month isalmost twice the value than that of the sol aged for one month. Theincrease of surface roughness is believed to be attributable to the factthat the particle size increases with an increase in aging time of sol.This belief is confirmed by the SEM measurement, in which an increase ofparticle size is seen for the sol with TEOS as the siloxane and acid asthe catalyst.

TABLE 14 Ra and Rm roughness of anti soiling substrates made by solswith different aged times Aged time, wt. % Ra Rm ID (M) of sol (nm) (nm)368-172-1 1 1 4.692 6.414 368-172-2 1 2 4.448 5.894 368-172-3 1 3 4.9266.225 368-174-1 8 1 10.332 13.436 368-174-2 8 2 8.938 11.654 368-174-3 83 6.788 9.155 Sol: Gen 1.5 Spin coating: 3000 rpm; 255 ramp; 30 sec; 0.5ml of sol Curing at 200° C. for 5 min

The durability of the coated substrates in the present example wasevaluated using a Thermal Cycle Test and a Condensing Humidity ChamberTest. Two coated substrates were evaluated in this present example. Thefirst substrate supported a coating made from a sol with TEOS, and thesecond substrate supported a coating made from a sol with a mixedsiloxane of TEOS and OTMOS.

Tables 15 and 16 summarize the calculated average total reflectionsbased on measured broadband reflections, and measured water contactangles before and after the two durability tests. Table 15 shows nosignificant change in the average total reflection on the substratesurface. Table 16 also shows no significant change in the water contactangle of the substrate surface coated by the sol with mixed TEOS andOTMOS. However, a large decrease of water contact angle was observed forsubstrates coated using the sol with only TEOS. The decrease on watercontact angle may be attributed to a damaged surface during the chambertest. The coating layer may have been hydrolyzed while exposed to theenvironment of high temperature and humidity. A more hydrophobic surfacemay have an added benefit of being resistant to silica hydrolysis. It isbelieved that this is the reason why a surface of substrate coated by amixed alkylsiloxane sol comprising TEOS and OTMOS may be more stablethan other alkylsiloxane coated substrates.

TABLE 15 Reflection of substrates coated by sol with differentalkylsiloxanes Chamber R % ID test Siloxane in sol pre post Change 368-Thermal Octyltrimethoxysiloxane 93.32 93.29 −0.03 180-1 cycle(OTMOS)/TEOS 50:50 wt. ratio 368- Thermal Tetraethyl orthosilicate 94.2293.28 −0.94 180-4 cycle (TEOS) 368- 85%/ Octyltrimethoxysiloxane 93.3892.95 −0.43 180-5 85° C. (OTMOS)/TEOS 50:50 wt. ratio 368- 85%/Tetraethyl orthosilicate 93.33 92.83 −0.49 180-8 85° C. (TEOS) Spincoating: 3000 rpm; 255 ramp; 30 sec; 0.5 ml of sol Test time: 5 day

TABLE 16 Water contact angle of substrates coated by sol with differentalkylsiloxanes Chamber Water contact angle ID test Siloxane in sol prepost change 368- Thermal Octyltrimethoxysiloxane 96.40 43.24 −53.16180-1 cycle (OTMOS)/TEOS 50:50 wt. ratio 368- Thermal Tetraethylorthosilicate 111.94 115.64 3.70 180-4 cycle (TEOS) 368- 85%Octyltrimethoxysiloxane 111.82 126.30 180-5 humidity/ (OTMOS)/TEOS 85°C. 50:50 wt. ratio 368- 85% Tetraethyl orthosilicate 96.88 33.48 −63.40180-8 humidity/ (TEOS) 85° C. Spin coating: 3000 rpm; 255 ramp; 30 sec;0.5 ml of sol Test time: 5 day

In order to appraise the process developed in the present example, arepeatability test was carried out using five pieces of anti-soilingsubstrates prepared using a sol with only TEAS. The average totalreflection calculated and water contact angles measured during therepeatability test are summarized in Table 17. FIG. 19 further clarifiesthe reflective properties of the coated substrates. The results showthat the average total reflection of the substrates may be as high as94.21%, and a water contact angle as high as about 100° may be achieved,in certain cases. The error range of the average total reflection isabout 0.06%, and the error range of the water contact angle is about 7°.

TABLE 17 Reflection and water contact angle of coated substrates fromrepeatability test R % coated ID substrate R % gain Water contact angle368-177-1 94.18 −0.06 112.58 106.61 115.43 368-177-2 94.17 −0.07 100.42111.92 99.91 368-177-3 94.25 0.01 105.05 107.98 109.07 368-177-4 94.290.05 112.56 120.56 109.76 368-177-5 94.16 −0.08 96.56 103.3 102.48 Avg.R % 94.21 −0.03 105.43 110.07 107.33 STD 0.06 0.06 7.17 6.63 6.19TEOS-only sol aged for one month R % of uncoated mirror: 94.24%

Observations from the presently disclosed example suggest that asubstrate surface coated with a sol composed of TEOS and OTMOS, cured ata shorter time, and aged at a shorter time, exhibit hydrophobicity. Thewater contact angle and durability measurements show that such acomposition and procedure may allow the water droplets to perform thedesired rolling action, thus making it possible to achieve anti-soilingproperties in some instances. The present example also shows a highR_(m) value on the surface after a long aging time may not achieve ahydrophobic property as suggested.

Certain example embodiments also may be conducted on other substrates,i.e. a soda lime silicate glass, and/or so-called low-iron glass.Low-iron glass is described in, for example, U.S. Pat. Nos. 7,893,350;7,700,870; 7,557,053; 6,299,703; and 5,030,594, and U.S. PublicationNos. 2006/0169316; 2006/0249199; 2007/0215205; 2009/0223252;2010/0122728; 2010/0255980; and 2011/0275506. The entire contents ofeach of these documents is hereby incorporated herein by reference.

As used herein, the terms “on,” “supported by,” and the like should notbe interpreted to mean that two elements are directly adjacent to oneanother unless explicitly stated. In other words, a first layer may besaid to be “on” or “supported by” a second layer, even if there are oneor more layers there between.

In certain example embodiments, a method of making a coated articlecomprising a glass substrate supporting a coating is provided. A sol iswet-applied, directly or indirectly, on a major surface of thesubstrate. The sol comprises at least first and second alkylsiloxanechemicals, with the first and second alkylsiloxane chemicals havingtetra-alkoxysiloxane and tri-alkoxysiloxane structures, respectively.The sol is dried and/or cured to form the coating. The sol is aged forno more than five months prior to the wet-applying.

In addition to the features of the previous paragraph, in certainexample embodiments, the alkylsiloxane chemicals may be provided atsubstantially equal weight percentages.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, the alkylsiloxane chemicals may be selectedfrom the group consisting of octyltrimethoxysiloxane (OTMOS),pentyltriethoxysiloxane (PTEOS), 3,3,3-trifluoropropyltrimethoxysiloxane (TFTMOS), tetraethyl orthosilicate (TEOS), andcombinations thereof.

In addition to the features of any of the three previous paragraphs, incertain example embodiments, the sol may be aged for less than or equalto 1 month prior to the wet-applying.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the coating may have a root mean squareroughness of 3-6.5 nm.

In addition to the features of any of the five previous paragraphs, incertain example embodiments, alkylsiloxane chains may protrude outwardlyfrom a surface of the coating.

In addition to the features of any of the six previous paragraphs, incertain example embodiments, alkylsiloxane groups may be hydrolyzedusing an acid catalysis process.

In addition to the features of the previous paragraph, in certainexample embodiments, the hydrolyzed alkylsiloxane groups may bepartially condensed to form a tetra-cyclic siloxane, e.g., providingnucleation sites for further growths to become three-dimensionalparticles on the coating.

In addition to the features of the previous paragraph, in certainexample embodiments, the three-dimensional particles may grow to 1-5 nmin major distance, with a precursor solution pH of 1-8.

In addition to the features of any of the nine previous paragraphs, incertain example embodiments, the coating may be a refractive index below1.3 and/or a thickness of 60-100 nm.

In addition to the features of any of the ten previous paragraphs, incertain example embodiments, the coating may be cured for less than 25minutes.

In addition to the features of any of the 11 previous paragraphs, incertain example embodiments, a water contact angle theta of the coatingmay be greater than about 100 degrees.

In certain example embodiments, a method of making a coated articlecomprising a glass substrate supporting a coating is provided. A sol iswet-applied, directly or indirectly, on a major surface of thesubstrate, with the sol comprising tetraethyl orthosilicate (TEOS) andoctyltrimethoxysiloxane (OTMOS). The sol is dried and/or cured to formthe coating. The coating has an initial contact angle of 100-131degrees.

In addition to the features of the previous paragraph, in certainexample embodiments, the coating may have a root mean square roughnessof 4-5 nm.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, TEOS and OTMOS may be provided in weightpercentages in the sol that differ from one another by no more than 5%.

In addition to the features of any of the three previous paragraphs, incertain example embodiments, the sol may be aged for no more than aboutfive months prior to the wet-applying.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the coating may have a refractive index ofless than 1.3.

In addition to the features of any of the five previous paragraphs, incertain example embodiments, the coating may be provided at a thicknessof 70-90 nm.

In addition to the features of any of the six previous paragraphs, incertain example embodiments, the coating may be cured for less than 15minutes.

In certain example embodiments, a method of making a mirror is provided.A thin film coating is disposed on a first major surface of thesubstrate, with the thin film coating having a reflectivity of at leastabout 85%. A sol is wet-applied, directly or indirectly, onto the thinfilm coating. The sol comprises at least first and second alkylsiloxanechemicals, with the first and second alkylsiloxane chemicals havingtetra-alkoxysiloxane and tri-alkoxysiloxane structures, respectively,and with the sol having been aged for no more than three months prior tothe wet-applying. The sol is dried and/or cured to form an anti-soilingcoating that at least initially has a contact angle of greater than 100degrees.

In addition to the features of the previous paragraph, in certainexample embodiments, reflection from the mirror may be no more than0.15% lower than the reflection would be if no anti-soiling coating werepresent.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, the alkylsiloxane chemicals may be selectedfrom the group consisting of octyltrimethoxysiloxane (OTMOS),pentyltriethoxysiloxane (PTEOS), 3,3,3-trifluoropropyltrimethoxysiloxane (TFTMOS), tetraethyl orthosilicate (TEOS), andcombinations thereof.

In addition to the features of any of the three previous paragraphs, incertain example embodiments, the anti-soiling coating may have arefractive index of less than 1.3.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the anti-soiling coating may have athickness of 60-100 nm.

In addition to the features of any of the five previous paragraphs, incertain example embodiments, the anti-soiling coating may have a curingtime of less than 25 minutes.

In certain example embodiments, a sol composition is provided. At leasttwo alkylsiloxane chemicals are provided at substantially the sameweight percents. A first alkylsiloxane chemical has atetra-alkoxysiloxane structure, and a second alkylsiloxane chemical hasa tri-alkoxysiloxane structure. The sol composition is aged less than 3months and has a cure time less than 10 minutes.

In addition to the features of the previous paragraph, in certainexample embodiments, the alkylsiloxane chemicals may be selected fromthe group consisting of octyltrimethoxysiloxane (OTMOS),pentyltriethoxysiloxane (PTEOS), 3,3,3-trifluoropropyltrimethoxysiloxane (TFTMOS), tetraethyl orthosilicate (TEOS, Aldrich),and combinations thereof.

In certain example embodiments, a coated article is provided. Amulti-layer thin film coating is disposed, directly or indirectly, on afirst major surface of a substrate, with the thin film coating having areflectivity of at least about 85%. A wet-applied anti-soiling coatingis formed from a sol aged for no more than about three months prior tothe wet application and comprising tetra-alkoxysiloxane andtri-alkoxysiloxane components at least initially provided insubstantially equal weight percents. The anti-soiling coating has aninitial contact angle theta greater than 100 degrees, a refractive indexless than 1.3, a thickness of 60-100 nm, and a root mean squareroughness of 3-6.5 nm.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. In certain embodiments, other experimentalprocedures, alkylsiloxane mixtures, and curing times may be used inconnection to one or a combination of the limitations described above.

1-28. (canceled)
 29. A method of making a coated article comprising aglass substrate supporting a coating, the method comprising:wet-applying a sol, directly or indirectly, on a major surface of thesubstrate, the sol comprising at least first and second alkylsiloxanechemicals, the first alkylsiloxane chemical comprising tetraethylorthosilicate (TEOS) and the second alkylsiloxane chemical comprising asiloxane other than TEOS, wherein the TEOS and the second alkylsiloxanechemical comprising a siloxane other than TEOS are provided in weightpercentages in the sol that differ from one another by no more than 5%;and drying and/or curing the sol to form the coating, the coating havinga root mean square roughness of 3-6.5 nm, wherein the sol is aged for nomore than five months prior to the wet-applying.
 30. The method of claim29, wherein the sol is aged for less than or equal to 1 month prior tothe wet-applying.
 31. The method of claim 29, wherein alkylsiloxanechains protrude outwardly from a surface of the coating.
 32. The methodof claim 29, wherein alkylsiloxane groups are hydrolyzed using an acidcatalysis process.